[The primary optical projection in albino and pigmented rats].

1. We have studied by silver degeneration methods in transversal and horizontal brain series the pathways and the terminal nuclei of the primary optic system in albino and pigmented rats. 2. About 90% of the retinal axons are crossing in the Chiasma opticum. Differences between albino and pigmented rats are small. At the level of the lateral geniculate body (l.g.b.) the axons ramify. One branch is going in the optic tract or in the transversalsystem to the pretectum and tectum. The other branch goes as a collateral in the longitudinal system of the dorsal l.g.b. and ends here. 3. The optic fibers project--especially contralateral--to the following nuclei: veutral l.g.b. (lateral half), dorsal l.g.b., nucleus of the optic tract, Nc. olivaris praetectalis, Ncc. praetectales anterior et posterior and superior colliculus (laminae I-III). In the nuclei of the pretectal region are ipsilateral only a few degenerating fibers. 4. Especially in the dorsal l.g.b. but also in the superior colliculus the pigmented rats show ipsilateral an larger retinal input. 5. The ipsilateral fibers project to a special region in the dorsal l.g.b. This region is also innervated by contralateral axons. 6. In both the albino and pigmented rats the dorsal l.g.b. shows no lamination in the cytoarchitectonical picture and the ipsi- and contralateral input regions overlap. Therefore in the rat we can not speak from a laminated dorsal l.g.b. We have here--prepoperantly functional caused--a simple form of l.g.b. 7. The accessory optic system is only decussated. It includes the Fasciculus inferior tr. opt. accessorius, who projects only and direct to the median terminal nucleus and the Fasciculus superior tr. opticus accessorius. The last goes off from the optic tract at the level of the pretectal region and innervates all the 3 accessory optic nuclei. 8. In a few preparates we found references for a direct retino-hypothalamic connection (Nc. suprachiasmaticus and Nc. arcuatus hypothalami).